The present invention generally relates to a file control system and a file control computer for use in such file control system, and in particular relates to a NAS system.
In recent years, since the capacity of files being used in corporations and the like is increasing drastically, the use of a NAS (Network Attached Storage) as a storage apparatus for storing files is becoming widespread.
A NAS includes a file system as a function for storing files in a memory device. A NAS creates storage areas (hereinafter also referred to as “volumes”) that are required in the file system from a storage medium such as an HDD (Hard Disk Drive). An administrator estimates the storage capacity that will be required in the file system before starting a NAS operation, and creates a volume of that storage capacity in the file system in advance.
Nevertheless, under the current circumstances where it is inevitable to drastically increase the capacity of a file system, it is difficult for an administrator to accurately estimate the storage capacity that is required in the file system in advance. To begin with, the allocation of a large capacity to a file system will lead to the wasted use of the storage medium.
Thus, Japanese Patent Laid-Open Publication No. 2005-11316 (Patent Document 1) discloses technology of automatically expanding the capacity of a file system according to the usage frequency of the storage capacity in the file system. With this technology, since a volume is automatically expanded in accordance with the capacity that is currently required by the file system, an administrator is not required to strictly estimate the capacity that is required in the file system.
Meanwhile, a significant feature of a NAS file system is that, in addition to the basic function of storing files, it includes functions (hereinafter referred to as the “additional functions”) that improve the administrator's convenience by managing the history and replication of files. For instance, Japanese Patent Laid-Open Publication No. 2004-342050 (Patent Document 2) discloses technology of storing images of a file system at a certain point in time. In addition, Japanese Patent Laid-Open Publication No. 2005-292952 (Patent Document 3) discloses technology of transferring contents of a file system to a remote site.
Moreover, “SAN & NAS Storage Network Management” by W. Curtis Preston, p. 108, Oreilly Japan, Oct. 30, 2002 (Non-Patent Document 1) discloses technology of realizing the mirroring of the file system through collaboration of the volume mirroring technology of the storage apparatus and the file system.